1. Field of the Invention
The present invention relates to a optical near-field generator and a near-field optical recording and reproduction apparatus having a optical near-field generator mounted in a head thereof.
2. Background Art
In recent years, a thermally assisted magnetic recording has been proposed as a means of realizing high recording densities of 1 Tb/in2 or greater (H. Saga, H. Nemoto, H. Sukeda, and M. Takahashi, Jpn. J. Appl. Phys. 38, Part 1, 1839 (1999)). In conventional magnetic recording apparatuses, there is the problem of loss of recorded information due to heat fluctuation as the recording density exceeds 1Tb/in2. In order to prevent this problem, it is necessary to increase the coercive force of the magnetic recording medium. However, since there is a limit to the magnitude of magnetic field that a recording head can produce, it becomes impossible to form a recording bit on the medium if the coercive force is increased too much. To solve this problem, in the thermally assisted magnetic recording, the medium is optically heated to reduce its coercive force at the moment of recording. In this way, it becomes possible to record in a high coercive force medium and to thereby realize recording densities of 1 Tb/in2 or higher.
In such thermally assisted magnetic recording apparatus, the spot size of the irradiating light needs to be on the same order as the size of the recording bit (several tens of nanometers) because larger optical spot sizes would eliminate the information in adjacent tracks. To heat such a microscopic region, optical near-field is used. Optical near-field is a localized electromagnetic field (light of which the wave number includes an imaginary component) that exists near a microscopic object of a size smaller than the wavelength of the light. It is produced by means of a microscopic aperture of a size smaller than the wavelength of the light or a metal scatterer. For example, the Technical Digest of 6th International Conference on Near Field Optics and Related Techniques, the Netherlands, Aug. 27-31, 2000, p. 55 proposes a optical near-field generator that employs a triangular metal scatterer as a high-efficiency optical near-field generator. When the metal scatterer is irradiated with light, plasmon resonance is excited in the metal scatterer, producing strong optical near-field at the apex of the triangle. Use of such optical near-field generator enables a highly efficient collection of light in a region of less than several tens of nanometers.
Non-patent Document 1: Jpn. J. Appl. Phys. 38, Part 1, 1839 (1999)
Non-patent Document 2: Technical Digest of 6th International Conference on Near Field Optics and Related Techniques, the Netherlands, Aug. 27-31, 2000, p. 55